The invention relates to an adjusting device for an adjustable vehicle seat which is provided with a first adjusting element and with a second adjusting element. The second adjusting element is motion-linked with the first adjusting element. The motion-linkage is either a swivelling linkage or a linear guiding. When designed as a linear guiding, the adjusting device is particularly conceived to serve as a for and aft adjustment device for an underframe of the vehicle seat relative to a seat part. The adjusting device has a threaded spindle and a spindle nut encompassing the spindle. The spindle is non rotatably fastened onto the first adjusting element of the adjusting device. The spindle nut is rotatably carried on the second adjusting element and forms on its outer case a worm wheel which meshes with a worm which in its turn may be connected to a multi turn actuation.
Such an adjusting device is known for example from DE 198 15 283 A.
The present invention constitutes a development of the European Patent Application 99 111 911 with priority date Aug. 12, 1998 which is not prepublished. The complete content of the disclosure of this European Application constitutes an inherent part of the present application.
The European Application already suggests having the spindle nut made of plastic. To have the spindle nut made of plastic provides on one side benefits for an advantageous accurate manufacturing and on the other side for a very silent run. A spindle nut made of plastic however does not have the stability of a spindle nut made of metal. Particularly in cases of loads occasioned by an accident and exerted onto the adjusting device, the spindle nut may expand or split. By a load occasioned by an accident a load is meant which exceeds the loads of normal driving and which triggers safety devices such as for example air bags, seat belt tighteners and the like. The situations dealt with here are such as arise in the event of an accident.
The present invention constitutes a development of the U.S. Pat. No. 6,260,922, issued Jul. 17, 2001. The complete content of the disclosure of this U.S. Patent constitutes an inherent part of the present application, and is hereby incorporated by reference.
The invention aims to permit to further use a nut made of synthetic and at the same time to somehow overcome the drawbacks, particularly those regarding the reduced stability over a metallic spindle nut.
On the basis thereof, it is the object of the present invention to develop the adjusting device of the type mentioned above so that the spindle nut may be made of synthetic material and is thereby reinforced with simple means in such a manner that splitting or expanding of the spindle nut in the event of longitudinal loading of the spindle is prevented or at least only occurs under much higher loads than if the measures according to the invention had not been taken.
The solution of this object is to provide an adjusting device for a vehicle seat having a first adjusting element and a second adjusting element that is motion-linked to the first adjusting element, particularly a length-adjustment device for an underframe of the vehicle seat relative to a seat part, whereas the adjusting device has a spindle and an associated spindle nut encompassing the spindle and whereas the spindle is non rotatably fastened onto the first adjusting element of the adjusting device and the spindle nut a) is rotatably carried in the second adjusting element, b) forms on its outer case a worm wheel that engages a worm which may be connected to a multi turn actuation, c) is made of synthetic material and d) is encompassed on either of its two axial end areas by a reinforcing barrel that encircles the corresponding end area of the spindle nut.
On this adjusting device, the spindle nut made of synthetic material is provided on either of its two axial end areas with one reinforcing barrel which encompasses the spindle nut and is non rotatably linked to it. The two reinforcing barrels are extending as far as admissible towards the central area of the spindle nut. That is, they extend so far toward the central area as they do not hinder the motion of the worm. The reinforcing barrels considerably enhance the stability of the spindle nut in its end areas, which increases the stability of the whole system.
The advantageous features of a spindle nut made of synthetic material are maintained. Mounting is not rendered more difficult. It is actually made even easier, as will be seen in the following. Finally, the two reinforcing barrels constitute a piece that is inexpensive and easy to manufacture and that, in a developed embodiment, may even be configured integral with a bearing shell of a terminal bearing for the spindle nut so that, while the additional mechanical expenditure for the reinforcing barrels is small, the achieved increase in rigidity is considerable.
In a preferred development the reinforcing barrel therefore is provided toward the end area of the spindle nut with an annular vault forming a bearing surface for a bearing. In particular, the bearing surface formed is that of a ball bearing. The bearing surface, which is needed anyway and which is formed on a bearing ring, is combined in this way with the reinforcing barrel to form one unique piece. The mounting of the bearing is thus made easier, while the expenditure is only slightly increased.
In a preferred development, a ring made of elastic material, particularly a spring lock washer or an O-ring made of rubber, is arranged between the reinforcing barrel and the spindle nut. It preferably is located in the transition area between the reinforcing barrel and the bearing surface. The reinforcing barrel is preferably directly connected to the spindle nut by its end pointing toward the central area of the spindle nut. Seen from there, the elastic means is provided outwardly axially, said means serving to attenuate the development of noise of the axially even farther outward located bearing and to achieve positioning.
The reinforcing barrel may preferably be pushed axially onto the spindle nut. This permits a very easy installation. It furthermore preferably has an outer diameter that corresponds to the outer diameter of the threaded section of the worm wheel. Accordingly, the reinforcing barrel does not require additional space, the reinforcing barrel may on the contrary be arranged externally to the meshing area of the worm in an area in which, according to prior art, threads are still provided.
In a preferred embodiment the reinforcing barrel is made of metal. The considerably higher rigidity is achieved in this way. The reinforcing barrel is preferably provided with a radially running area that has got the shape of a circular ring. This area may also be omitted though. The essential part is an axially running casing area which is essentially cylindrical.
In another preferred embodiment, the spindle nut is encompassed by a plastic casing that receives at its ends bearings for carrying and positioning the spindle nut. This plastic casing may be manufactured at low cost, it additionally is light and reduces noise. In a preferred development it is encompassed by a holder made of metal which is essentially U-shaped. This holder on one side provides for mechanical stability, on the other it may bend under loads occasioned by an accident and as a result interlock at the spindle, thus contributing to its stability in case of loads occasioned by an accident.